A problem in the field of implants relates to bone growth and notably arthrodesis, i.e. the bone merging of two structures, such as for example vertebrae. Indeed, it is sometimes sought to obtain merging of at least two vertebrae for example when at least one of their adjacent intervertebral discs is lesioned. Various arthrodesis techniques are known from the prior art, based on various types of implants such as for example intersomatic cages (or arthrodesis cages) inserted in the place of a disc in order to promote bone growth, or arthrodesis plates attached on both vertebrae in order to immobilize them and allow arthrodesis, or further osteosynthesis or arthrodesis rods, used for immobilizing the vertebrae, to which they are generally connected through pedicular screws or hooks, or finally inter-spinal implants inserted between the spines of the vertebrae (or “spineous apophyses”) for immobilizing them and thereby facilitating merging. These types of implants aim at finding an answer to a problem known in the field which is to stabilize the vertebral level to be treated. Solutions are also known, notably at the lumbar and sacral level, using facet implants allowing such stabilization, by attaching the articular facets with the purpose of obtaining merging. For example, implants are known from the prior art, such as for example from patent FR272617161, in the form of a hollow cylinder provided with threading for screwing bones, forming a screw in which a conduit and grooves are made in order to provide a grafting space allowing the insertion of tissue or bone substitute or cement for facilitating the merging of the structures in which the screw is implanted. It will be noted that vertebral articular apophyses (or articular processes or pedicular facets) are designated here by the term of “articular facet”, since each vertebra is jointed with the one above and below through articular facets which are posterior and the invention is useful for treating these articular facets, but it is possible to optionally use various embodiments on other structures, notably vertebral structures, such as for example costal or sacro-illiac facets if need be. Articular apophyses protrude above and below the base of transverse apophyses of the vertebrae, behind the pedicles. At the lumbar level for example, the upper articular apophyses are separated from each other by a more considerable distance than that which separates the lower two. The articular facets which they support have the shape of a vertical gutter, the concavity of which faces rearwards and inwards, a gutter in which will be placed the lower articular apophyses, which have a convex articular surface in the opposite direction, i.e. forwards and outwards. The lower articular apophyses provide a convex articular surface in the form of a cylinder segment, which faces outwards and slightly forwards. This surface slides in the concavity of the upper articular apophysis of the vertebra located below. These structures are therefore important for the stability of the vertebrae one on the other and it will moreover be noted that the bone deficit (or “lysis”) of the isthmuses (or “pars interarticularis”) located at their base is often responsible for spondilolysthesis (the sliding of a vertebra relatively to the other adjacent ones) which generally lead to degeneration of intervertebral discs. When it is sought to achieve vertebral arthrodesis, it is therefore sometimes desirable to use a facet implant for attaching the lower articular apophyses of a vertebra to the upper articular apophyses of the adjacent vertebra. These facet implants may either be “inter-facet” implants, i.e they are inserted between the articular surfaces, or “trans-facet” implants, i.e. they are inserted through the articular apophyses for attaching the articular surfaces together. Inter-facet implants are generally set into place in the articular joint by identifying the approach axis and for example by positioning a broach used as a guide for the implant, which is often cannulated (i.e. hollow). A problem in the field relates to the solidity since it is desirable to guarantee the integrity of the implant in spite of its small size and its often recessed layout.
A problem relating to implants in general, in particular spinal implants and notably facet implants, relates to the stability of the implant. It is required that an implant be stable in its implantation site, in particular when arthrodesis is desired since the latter should take place in a relative position of the elements of the rachis, which is optimum. Stabilization and/or locking of the implant is(are) therefore often preferable. Another general problem relates to the ease and/or the rapidity of the implantation. Further, it is generally desired that the implants may be implanted with minimum invasiveness, i.e. it is sought to limit the size of the incisions and of the damages on the surrounding tissues. Percutaneous solutions or only requiring a few millimeters of incision (for example 2 to 40 mm) are often sought. Further, it is generally desirable to limit resorting to imaging in order to avoid exposing the patients to rays.
Intra-facet implants, often accompanied by other problems such that, for example, the requirement of providing the graft or bone substitute or cement for facilitating the merging, for example by means of the presence of a grafting chamber in the implant, in spite of its small size, and by maintaining sufficient rigidity of the implant in order to support the forces between both fixed facets. Further, it is generally desirable to tap, clean out or sharpen the articular surfaces, for example in order to remove cartilage and/or promote bone growth.
Transfacet implants, which often provide the advantages of being simple, being able to be used percutaneously and allowing compression of articular facets against each other, are often accompanied by other problems such as for example, the lack of sharpening, cleaning or tapping of the articular joints, which limits the bone growth rate. These implants generally include at least one implanted screw with an aim through articular surfaces (transfacet). They are generally also guided by a broach but they generally require that the bone be perforated beforehand, often percutaneously by means of a bit. It is possible to tap the bone around the broach in order to screw in the implant (often “cannulated”, i.e. hollow and slipped around the broach) which generally includes a bone thread (e.g., a threading adapted for screwing into bone tissue), for example for not risking any fracturing of the facets during the setting into place. Finally, it is generally desirable that these implants include a stabilization means (of either one of the facet or both facets) and/or a compression and/or locking means and/or bone supporting means which will spread the loads over at least one of the facets (notably the posterior facet) at the end of the screwing.
The diversity of the problems, notably of those discussed above, is generally accompanied by the problem that a same implant cannot be equally used as a transfacet implant and as an interfacet implant, which forces the provision of various types of implants and instruments.
In this context, it is interesting to propose a solution with which it is possible to efficiently provide an answer to said at least one portion of these problems.